Hyperlipidemia and Arteriosclerosis
Cardiovascular, cerebrovascular, and peripheral vascular diseases are responsible for a significant number of deaths annually in many industrialized countries. One of the most common pathological processes underlying these diseases is arteriosclerosis. Arteriosclerosis is characterized by lesions, which begin as localized fatty thickenings in the inner aspects of blood vessels supplying blood to the heart, brain, and other organs and tissues throughout the body. Over time, these atherosclerotic lesions may ulcerate, exposing fatty plaque deposits that may break away and embolize within the circulation. Atherosclerotic lesions obstruct the lumens of the affected blood vessels and often reduce the blood flow within the blood vessels, which may result in ischemia of the tissue supplied by the blood vessel. Embolization of atherosclerotic plaques may produce acute obstruction and ischemia in distal blood vessels. Such ischemia, whether prolonged or acute, may result in a heart attack or stroke from which the patient may or may not recover. Similar ischemia in an artery supplying an extremity may result in gangrene requiring amputation of the extremity.
For some time, the medical community has recognized the relationship between arteriosclerosis and levels of dietary lipid, serum cholesterol, and serum triglycerides within a patient's blood stream. Many epidemiological studies have been conducted revealing that the amount of serum cholesterol within a patient's blood is a significant predictor of coronary disease. Similarly, the medical community has recognized the relationship between hyperlipidemia and insulin resistance, which can lead to diabetes mellitus. Further, hyperlipidemia and arteriosclerosis have been identified as being related to other major health problems, such as obesity and hypertension. Hyperlipidemia may be treated by changing a patient's diet. However, use of a patient's diet as a primary mode of therapy requires a major effort on the part of patients, physicians, nutritionists, dietitians, and other health care professionals and thus undesirably taxes the resources of health professionals. Another negative aspect of this therapy is that its success does not rest exclusively on diet. Rather, success of dietary therapy depends upon a combination of social, psychological, economic, and behavioral factors. Thus, therapy based only on correcting flaws within a patient's diet is not always successful.
In instances when dietary modification has been unsuccessful, drug therapy has been used as an alternative. Such therapy has included use of commercially available hypolipidemic drugs administered alone or in combination with other therapies as a supplement to dietary control. Hypolipidemic drugs have had varying degrees of success in reducing blood lipid; however, none of the hypolipidemic drugs successfully treats all types of hyperlipidemia. While some hypolipidemic drugs have been fairly successful, the medical community has not found any conclusive evidence that hypolipidemic drugs cause regression of atherosclerosis. In addition, all hypolipidemic drugs have undesirable side effects. As a result of the lack of success of dietary control, drug therapy and other therapies, atherosclerosis remains a major cause of death in many parts of the world.
To combat this disturbing fact, a relatively new therapy has been used to reduce the amount of lipid in patients for whom drug and diet therapies were not sufficiently effective. This therapy, referred to as plasmapheresis therapy or plasma exchange therapy, involves replacing a patient's plasma with donor plasma or more usually a plasma protein fraction. While having been fairly successful, this treatment has resulted in complications due to introduction of foreign proteins and transmission of infectious diseases. Further, plasma exchange undesirably removes many plasma proteins, such as very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL).
HDL is secreted from both the liver and the intestine as nascent, disk-shaped particles that contain cholesterol and phospholipids. HDL is believed to play a role in reverse cholesterol transport, which is the process by which excess cholesterol is removed from tissues and transported to the liver for reuse or disposal in the bile. Therefore, removal of HDL from plasma is not desirable.
Other apheresis techniques exist that can remove LDL from plasma. These techniques include absorption of LDL in heparin-agarose beads (affinity chromatography), the use of immobilized LDL-antibodies, cascade filtration absorption to immobilize dextran sulphate, and LDL precipitation at low pH in the presence of heparin. Each method removes LDL but not HDL.
LDL apheresis, however, has disadvantages. For instance, significant amounts of plasma proteins in addition to LDL are removed during apheresis. In addition, LDL apheresis must be performed frequently, such as weekly, to obtain a sustained reduction in LDL-cholesterol. Furthermore, LDL removal may be counterproductive because low LDL levels in a patient's blood may result in increased cellular cholesterol synthesis. Thus, removal of LDL from a patient's blood may have negative side effects.
Yet another method of achieving a reduction in plasma cholesterol in homozygous familial hypercholesterolemia, heterozygous familial hypercholesterolemia and patients with acquired hyperlipidemia is an extracorporeal lipid elimination process, referred to as cholesterol apheresis. In cholesterol apheresis, blood is withdrawn from a patient, the plasma is separated from the blood, and the plasma is mixed with a solvent mixture. The solvent mixture extracts lipids from the plasma. Thereafter, the delipidated plasma is recombined with the patient's blood cells and returned to the patient.
More specifically, lipid apheresis results in the removal of fats from plasma or serum. However, unlike LDL apheresis, the proteins (apolipoproteins) that transport lipids remain soluble in the treated plasma or serum. Thus, the apolipoproteins of VLDL, LDL and HDL are present in the treated plasma or serum. These apolipoproteins, in particular apolipoprotein A1 from the delipidated HDL in the plasma or serum, are responsible for the mobilization of unwanted lipids or toxins, such as excessive amounts of deposited lipids including cholesterol in arteries, plaques, and excessive amounts of triglycerides, adipose tissue, and fat soluble toxins present in adipose tissue. These excessive amounts of lipids or toxins are transferred to the plasma or serum, and then bound to the newly assembled apolipoproteins. Application of another lipid apheresis procedure successively removes these unwanted lipids or toxins from the plasma and thus the body. The main advantage of this procedure is that LDL and HDL are not removed from the plasma. Instead, only cholesterol, some phospholipid and a considerable amount of triglycerides are removed.
While lipid apheresis has the potential to overcome the shortcomings of dietary control, drug therapy and other apheresis techniques, existing apparatuses and methods for lipid apheresis do not provide a sufficiently rapid and safe process. Thus, a need exists for systems, apparatuses and methods capable of conducting lipid apheresis more quickly than accomplished with conventional equipment and methods.
Unfortunately, existing lipid apheresis systems suffer from a number of disadvantages that limit their ability to be used in clinical applications, such as in doctors' offices and other medical facilities. One disadvantage is the explosive nature of the solvents used to delipidate this plasma. If used in a continuous system, these solvents are in close proximity to patients and medical staff. Thus, it would be advantageous to limit this exposure; however, this hazard is clearly present for the duration of the delipidation process, which usually runs for several hours.
Another disadvantage is the difficulty in removing a sufficient amount of solvents from the delipidated plasma in order for the delipidated plasma to be safely returned to a patient. In addition, patients are subjected to an increased chance of prolonged exposure to solvents in a continuous system. Furthermore, current techniques do not provide for sequential multi-washes because the volume of blood necessary for continuous processing using conventional equipment requires removal of an amount of blood that would harm the patient. In other words, conventional equipment does not allow for automated continuous removal, processing and return of plasma to a patient in a manner that does not negatively impact total blood volume of the patient. While the long-term toxicity of various extraction solvents is not known, especially when present in the bloodstream, clinicians know that some solvents may cross the blood-brain barrier. Furthermore, external contact with solvents is known to cause clinical symptoms, such as irritation of mucous membranes, contact dermatitis, headaches, dizziness and drowsiness. Therefore, conventional equipment for lipid apheresis is not adequate to conduct continuous processing of a patient's blood.
Infectious Disease
While the medical community has struggled to develop cures for hyperlipidemia and arteriosclerosis, it has likewise struggled in its battle against infectious diseases. Infectious diseases are a major cause of suffering and death throughout the world. Infectious disease of varied etiology affects billions of animals and humans each year and inflicts an enormous economic burden on society. Many infectious organisms contain lipid as a major component of the membrane that surrounds them. Three major classes of organisms that produce infectious disease and contain lipid in their cell wall or envelope include bacteria, viruses, and protozoa. Numerous bacteria and viruses that affect animals and humans cause extreme suffering, morbidity and mortality. Many bacteria and viruses travel throughout the body in fluids, such as blood, and some reside in plasma. These and other infectious agents may be found in other fluids, such as peritoneal fluid, lymphatic fluid, pleural fluid, pericardial fluid, cerebrospinal fluid, and in various fluids of the reproductive system. Disease can be caused at any site bathed by these fluids. Other bacteria and viruses reside primarily in different organ systems or in specific tissues, where they proliferate and enter the circulatory system to gain access to other tissues and organs.
Infectious agents, such as viruses, affect billions of people annually. Recent epidemics include the disease commonly known as acquired immune deficiency syndrome (AIDS), which is believed to be caused by the human immunodeficiency virus (HIV). This virus is rapidly spreading throughout the world and is prevalent in various sub-populations, including individuals who receive blood transfusions, individuals who use needles contaminated with the disease, and individuals who contact infected fluids. This disease is also widespread in certain countries. Currently, no known cure exists.
It has long been recognized that a simple, reliable and economically efficient method for reducing the infectivity of the HIV virus is needed to decrease transmission of the disease. Additionally, a method of treating fluids of infected individuals is needed to decrease transmission of the virus to others in contact with these fluids. Furthermore, a method of treating blood given to blood banks is needed to decrease transmission of the virus to individuals receiving transfusions. Moreover, an apparatus and method are needed for decreasing the viral load of an individual or an animal by treating the plasma of that individual and returning the treated plasma to the individual such that the viral load in the plasma is decreased.
Other major viral infections that affect animals and humans include, but are not limited to meningitis, cytomegalovirus, and hepatitis in its various forms. While some forms of hepatitis may be treated with drugs, other forms have not been successfully treated in the past.
At the present time, most anti-viral therapies focus on preventing or inhibiting viral replication by manipulating the initial attachment of the virus to the T4 lymphocyte or macrophage, the transcription of viral RNA to viral DNA and the assembly of new virus during reproduction. Such a focus has created major difficulty with existing treatments, especially with regard to HIV. Specifically, the high mutation rate of the HIV virus often renders treatments ineffective shortly after application. In addition, many different strains of HIV have already become or are becoming resistant to anti-viral drug therapy. Furthermore, during anti-viral therapy, resistant strains of the virus may evolve. Finally, many common therapies for HIV infection involve several undesirable side effects and require patients to ingest numerous pills daily. Unfortunately, many individuals are afflicted with multiple infections caused by more than one infectious agent, such as HIV, hepatitis and tuberculosis. Such individuals require even more aggressive and expensive drugs to counteract disease progression. Such drugs may cause numerous side effects as well as multi-drug resistance. Therefore, an effective method and apparatus is needed that does not rely on drugs for combating infections organisms found in fluids. Such a method should reduce the infectivity of infectious organisms.
Thus, a need exists to overcome the deficiencies of conventional systems and methods for removing lipids from fluids, such as plasma or serum, and for removing lipids from infectious organisms contained in a fluid. Furthermore, a need exists for an apparatus and method to perform delipidation rapidly, either in a continuous or discontinuous manner of operation. A need further exists for such an apparatus and process to perform safely and reliably, and to produce delipidated fluid having residual plasma solvent levels meeting acceptable standards. In addition, a need exists for an apparatus having minimal physical connection between a patient and the lipid apheresis process. Furthermore, a need exists for an economical medical apparatus that is sterile and made of a disposable construction for a single use application. Finally, a need exists for such an apparatus and process to be automated, thereby requiring minimal operator intervention during the course of normal operation.